New analytical solutions for modified polarization saturation models in piezoelectric materials

Meccanica - In this paper, we present new analytical solutions for modified polarization saturation (PS) models for arbitrary polarized and semipermeable 2-D piezoelectric media. The PS model is...     

Coupled fire dynamics and thermal response of complex building structures

Simulation of the effects of severe fires on the structural integrity of buildings requires a close coupling between the gas phase energy release and transport phenomena, and the stress analysis in the load-bearing materials. The connection between the two is established primarily through the interaction of the radiative heat transfer between the solid and gas phases with the conduction of heat through the structural elements. This process is made difficult in large, geometrically complex buildings by the wide disparity in length and time scales that must be accounted for in the simulations. A procedure for overcoming these difficulties used in the analysis of the collapse of the World Trade Center towers is presented. The large scale temperature and other thermophysical properties in the gas phase are predicted using the NIST Fire Dynamics Simulator. Heat transfer to subgrid scale structural elements is calculated using a simple radiative transport model that assumes the compartment is locally divided into a hot, soot laden upper layer and a cool relatively clear lower layer. The properties of the two layers are extracted from temporal averages of the results obtained from the Fire Dynamics Simulator. Explicit formulae for the heat flux are obtained as a function of temperature, hot layer depth, soot concentration, and orientation of each structural element. These formulae are used to generate realistic thermal boundary conditions for a coupled transient three-dimensional finite element code. This code is used to generate solutions for the heating of complex structural assemblies.     

On martingale characterizations for some generalized space fractional Poisson processes

We obtain martingale characterizations for the generalized space fractional Poisson process (GSFPP) and for counting processes with Bern?tein intertimes. These serve as extensions of the Watanabe's characterization for the classical homogenous Poisson process. The corresponding assertion for the space fractional Poisson process (SFPP) is obtained as a particular case of our results.     

Electroanalytical Sensor for Diabetic Foot Ulcer Monitoring with Integrated Electronics for Connected Health Application

L‐tyrosine is an amino acid, the concentration of which is found to be highly elevated in patients suffering from diabetic foot ulcer (DFU). The latter proves to be fatal when it turns out chronic and may lead to amputation. The conventional clinical diagnostic methods are costly and time consuming, in which case, the condition of patient(s) may deteriorate long before proper treatment commences. Herein, we report the development of smart band‐aid for real time monitoring of L‐tyrosine by employing enzymatic bio‐sensor using α‐MnO₂/tyrosinase. The smart band‐aid was further integrated with portable electronics capable of wireless data transmission to a personal digital assistant, and its tyrosine sensing performance was evaluated. Anodic current was found to vary linearly with the concentrations of L‐tyrosine in the range of 5 nM–500 μM. The developed sensor displayed a limit of detection and sensitivity of 0.71 nM and 0.67 μA/nM/mm² respectively, with a stability of 25 days. The developed sensor was validated using a commercial impedance analyzer. The impedance response was found to be consistent with the cyclic voltammogram obtained and demonstrated to be a linear function of tyrosine concentration. The developed sensing platform combines early diagnosis with connected health technologies, thus, fitting well into modern healthcare needs.     

Effects of hypochlorite treatment on the surface morphology and mechanical properties of polyethersulfone ultrafiltration membranes

Polyethersulfone membranes are widely used for ultrafiltration and microfiltration especially in the dairy industry, but they are believed to degrade when exposed to the sodium hypochlorite solution that is used to sanitize the processing equipment. Such membranes were exposed to sodium hypochlorite for up to 25,000 ppm-day at 55 °C, and pH 9 and 12. Mechanical properties as measured by dynamic mechanical analysis and tensile strength did not change greatly, but surface properties measured by FTIR-ATR, field emission scanning electron microscopy and associated energy dispersive X-ray spectroscopy detected significant changes in the surface. Surface pitting was observed and was found to be most severe at pH 9. It was thought that pitting was the likely cause of degradation in performance of the membranes and that pits could act as stress raisers leading to cracking.     

Temperature-dependent volumetric and viscometric properties of amino acids in aqueous solutions of an antibiotic drug

Volumetric and viscometric properties of glycine and methionine (amino acids) in a 0.2 vol. % amikacin sulphate (antibiotic drug) aqueous solution with the molality range of 0.025 mol kg^?1–0.25 mol kg^?1 were measured over the temperature range of 20°C–40°C at the interval of 5°C. Different parameters like apparent molar volume (? _V), apparent molar adiabatic compression (? _κ ), isentropic compression (κ _S) along with other acoustical parameters were calculated. Parameters like viscous relaxation time (τ), free volume (V _F), internal pressure (Π _I), and molar cohesive energy (MCE) were calculated from dynamic viscosity measurements. The ? _V values are positive in both cases, but with higher magnitude observed in methionine. These positive values of ? _V are indicative of strong solute-solvent interactions at all temperatures. In case of methionine there is a sharp initial increase in the ? _V values which become almost constant with further additions of the amino acid. Structural differences in the two amino acids studied are clearly reflected in the different nature of the plots of different parameters. In case of an amino acid-drug system, dynamic viscosity increase has been attributed to the increase in the hydrophilic-ionic and hydrophilic-hydrophilic interactions with the increase in the amino acid concentration which in turn may cause more frictional resistance to the flow of the solution. All other parameters are discussed in terms of solute-solvent and solvent-solvent interactions.     

Synthesis and characterization of glycol-modified vanadium(V) oxoisopropoxide and their oximato derivatives: sol–gel transformations of [VO(OPr i )3], [VO{OCH2CH2OCH2CH2O}{OPr i }] and [VO{OCH2CH2OCH2CH2O}{ON=C(CH3)(C4H3S-2)}] to vanadia

Reaction of [VO(OPr ⁱ )₃] (1) with [O(CH₂CH₂OH)₂] in 1:1 molar ratio in anhydrous benzene yield glycol-modified precursor, [VO{OCH₂CH₂OCH₂CH₂O}{OPr ⁱ }] (2). Further reactions of (2) with internally functionalized oximes in anhydrous benzene yield heteroleptic complexes of the type [VO{OCH₂CH₂OCH₂CH₂O}{ON=C(R)(Ar)}] (3–8) {where R=CH₃, Ar=C₄H₃O-2 (3), C₄H₃S-2 (4), C₅H₄N-2 (5); and when R=H, Ar=C₄H₃O-2 (6), C₄H₃S-2 (7), C₅H₄N-2 (8)}. All these derivatives have been characterized by elemental analyses, molecular weight measurements and spectroscopic techniques. The crysoscopic molecular weight measurement as well as FAB mass study suggests dimeric nature of (2). However, FAB mass spectrum of (4), and the crysoscopic molecular weight measurements of (3), (4), (5) and (6) indicate the monomeric behavior of the oximato derivatives (3–8). Hexa-coordination around vanadium(V) has been proposed for both monomeric and dimeric derivatives. Sol–gel transformations of (1), (2) or (4) to vanadia [(a), (b) or (c), respectively] have been carried out at low sintering temperature (600 °C). The XRD patterns of (a), (b) or (c) indicate formation of a single orthorhombic phase in all the three cases. The SEM images suggest grain like [for (a) and (b)] and rod like [for (c)] morphology of the crystallites. IR, Raman spectra as well as EDX analyses indicate formation of pure vanadia. Absorption spectra of the vanadia (b) and (c) suggest energy band gaps of 2.53 and 2.65 eV, respectively.     

Zinc and iron determination in serum and urine samples of thyroid patients using cloud point extraction

A simple and rapid cloud point extraction method was applied for preconcentration of trace quantities of zinc (Zn) and iron (Fe) in biological samples (serum and urine) of thyroid patients prior to determination by flame atomic absorption spectrometry. The metals in serum and urine samples were complexed with 1-(2-thiazolylazo)-2-naphthol and entrapped in the surfactant octylphenoxypolyethoxyethanol (Triton X-114). After centrifugation, the surfactant-rich phase was diluted with 0.1 M HNO3 in methanol. For optimum recovery of analytes, the influences of the analytical parameters, including pH and amounts of complexing and surfactant reagents, were investigated. Enrichment factors of 66.4 and 70.2 were obtained for the preconcentration of Zn(II) and Fe(III), respectively. The obtained results showed sufficient recoveries (>98%) for Zn(II) and Fe(III) in certified reference materials (CRMs). The proposed method was applied to the determination of Zn(II) and Fe(III) in biological (serum and urine) samples and CRMs.     

The effect of cesium metal clusters on the optical properties of cesium iodide thin films

Cesium metal clusters strongly affect the optical properties of cesium iodide thin films. The metal clusters are formed during film formation by thermal evaporation. The cesium cluster of 30–40 nm in the matrix of cesium iodide insulating thin films results in Surface Plasmon Resonance (SPR). The peak position of these SPR peaks showed a red shift. This was shown to be due to changes in the dielectric constant of CsI resulting from the strains in the films caused by the metal clusters themselves.